The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 199 51 794.0, filed on Oct. 27, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a process for dewatering a fibrous material web, e.g., a paper or cardboard web, in which the fibrous material web is guided through a dewatering zone in which it is at least partially dewatered by being impacted with pressurized displacement gas. Moreover, the present invention relates to a device for dewatering the fibrous material web a dewatering zone in which the fibrous material web is at least partially dewatered by being impacted by pressurized displacement gas.
2. Discussion of Background Information
Water can be removed from a paper web using a differential gas pressure. This process is referred to as displacement dewatering. In this process, the water located in the pores between the fibers is blown out of the bonded-web fabric. In comparison to conventional wet presses in a single- or double-felt roll nip, the finished paper has a higher specific volume at the same dry content as after mechanical dewatering. With the aid of the displacement dewatering process, other important characteristics of the finished fibrous material web, such as bending stiffness, porosity, and opacity, can be positively influenced (J. D. Lindsay: xe2x80x9cDisplacement Dewatering to Maintain Bulk,xe2x80x9d Paperi ja Puu Vol. 74/No. 3/1992). A corresponding device arrangement for the displacement dewatering process has also already been suggested (W. Kawka and E. Szwarcztajn: xe2x80x9cSome Results of Investigations on the Equipment for Intensive Dewatering and Drying of Porous Papers,xe2x80x9d EUCEPA-79 International Conference, Paper 31, Page 153).
If a membrane is placed over the paper on the side of the gas pressure, a compression of the paper will occur as a result of the decrease in pressure in the membrane. Water is pressed out of the fibers into the pores between the fibers. This water is blown out of the pores by the differential gas pressure. According to the invention, when a membrane is used, a higher dry content is achieved (Kari Rxc3xa4isanen: xe2x80x9cHigh-Vacuum Dewatering on a Paper Machine Wire Section: A Literature Review,xe2x80x9d Paperi ja Puu, Vol. 78, No. 3, 1996).
The size of this compression depends on the relationship between the permeability of the membrane and of the bonded-web fabric. With a targeted compression, dry content and specific volume of the finished fibrous material web can be adjusted. In practice, however, the compression of the bonded-web fabric can be controlled only with difficulty because membrane permeability is difficult to change during operation of the production facility. Thus, in the case of otherwise identical process conditions, a certain dry content and a certain volume result at a certain gas pressure.
The present invention is directed to a process and a device of the type generally discussed above in which the process parameters of the displacement dewatering process can be deliberately adjusted and, correspondingly, the results of the displacement dewatering process, with regard to the dry content achieved and to the paper-related characteristics of the finished product, e.g., specific volume, porosity, surface roughness, and/or the like, can be intentionally influenced.
With regard to the process, the present invention includes impacting the fibrous material web with several gas pressure pulses one after another inside the dewatering zone.
Due to this construction, the bonded-web fabric, which has viscoelastic characteristics, is only compressed to a limited extent. If it is taken into account that the compression of the bonded-web fabric is accompanied by a reduction in flow resistance, it is possible, by making the impact with pressure correspondingly shorter, to prevent the bonded-web fabric from becoming too strongly compressed, which could result in the necessary amount of gas being unable to be pressed through the bonded web fabric.
In a suitable practical embodiment, the fibrous material web is guided through several displacement dewatering units within the dewatering zone.
The level of the pressure of at least one gas pressure pulse is advantageously adjustable, and, more suitably, the pressures of the various gas pressure pulses are adjustable separately from one another. If the fibrous material web is guided through several displacement dewatering units arranged at a distance from one another within the dewatering zone, the prevailing pressures in the various displacement dewatering units are advantageously correspondingly adjustable.
In this way, the amount of compression can be adjusted at least partially by, e.g, the level of the prevailing pressure in the respective displacement dewatering units.
Thus, by an individual control of the gas pressure pulses, the dewatering process can be controlled and characteristics such as dry content, density, porosity, and/or the like can be influenced.
In a suitable practical embodiment, the fibrous material web is guided through the dewatering zone along with the membrane, and the fibrous material web is impacted by the displacement gas through the membrane. In principle, however, the displacement gas dewatering according to the present invention can also occur without such a membrane.
Preferably, the fibrous material web, which is being impacted by displacement gas from one side, is guided through the dewatering zone along with at least one wire or felt belt arranged on the other side of the web.
In principle, it is also possible to guide the fibrous material web through at least one displacement dewatering unit within the dewatering zone whose gas pressure is pulsing, i.e., changes over time, and, preferably, at a certain frequency.
In the device according to the invention, the fibrous material web can be impacted by several gas pressure pulses one after the other within the dewatering zone.
The dewatering devices of the various dewatering units can be different and, e.g., run from top to bottom in an alternating fashion.
On the side of the fibrous material web facing away from the gas pressure, a fabric can be arranged that forms a blocking layer. This blocking layer allows the dewatered fluid through. in only one direction, i.e., from the fibrous material web to the felt (anti-rewetting fabric). The blocking layer can be integrated into the felt.
The present invention is directed to a process for dewatering a fibrous material web. The process includes guiding the fibrous material web through a dewatering zone, and directing a plurality of gas pressure pulses of a pressurized displacement gas one after the other onto a surface of the fibrous material web within the dewatering zone.
In accordance with a feature of the instant invention, the fibrous material web can include one of a paper and a cardboard web.
Further, a plurality of displacement dewatering units may be arranged within the dewatering zone at a distance from each other, and the process can further include guiding the fibrous material web through the plurality of displacement dewatering units. The. plurality of dewatering units arranged at a distance from each other may be sequentially arranged in a web travel direction. The process can also include adjusting-the pressures in the plurality of dewatering units.
According to another feature of the present invention, the process may include adjusting a pressure level of at least one of the plurality of gas pressure pulses. The process can also include separately adjusting pressure levels of the plurality of gas pressure pulses.
In accordance with still another feature of the invention, the process can further include guiding the fibrous material web through the dewatering zone along with a membrane, and directing the plurality of gas pulses onto the surface of the fibrous material web through the membrane.
According to a further feature of the instant invention, the process can further include guiding the fibrous material web through the dewatering zone along with at least one of a wire and felt belt, which is arranged on a side of the fibrous material web opposite the surface onto which the plurality of gas pulses are directed.
Inside the dewatering zone, the fibrous material web may be guided through at least one displacement dewatering unit, and the process may further include changing a gas pressure pulse in the at least one displacement dewatering unit over time. The gas pressure pulse in the at least one displacement dewatering unit can change at a certain frequency.
The present invention is directed to an apparatus for dewatering a fibrous material web in a dewatering zone. The apparatus includes a device for forming a plurality of gas pressure pulses which are arranged one after the other within the dewatering zone. The plurality of gas pressure pulses are directed onto a surface of the fibrous material web. The fibrous material web can include one of a paper and a cardboard web.
According to a feature of the instant invention, the device for forming the plurality of gas pressure pulses may include a plurality of displacement dewatering units arranged at a distance from one another within the dewatering zone. The to plurality of displacement dewatering units can be arranged one after the other in a web travel direction. Further, pressures inside the plurality of displacement dewatering units may be adjustable.
In accordance with another feature of the invention, a level of pressure of at least one of the plurality of gas pressure pulses can be adjustable. Pressures of the plurality of gas pressure pulses may be adjusted separately from one another.
A membrane can be arranged to be guided through the dewatering zone with the fibrous material web. The plurality of gas pressure pulses can be directed onto the surface of the fibrous material web through the membrane.
Moreover, at least one of a wire and a felt belt can be arranged to be guided through the dewatering zone with the fibrous material web. The at least one wire and felt belt may be arranged on a side of the fibrous material web opposite the surface onto which the plurality of gas pressure pulses are directed.
The device for forming a plurality of gas pressure pulses can include at least one displacement dewatering unit having gas pressure pulses which are changeable over time. The gas pressure pulses can be changeable at a certain frequency.
The present invention is directed to an apparatus for dewatering a web in a dewatering zone. The apparatus includes a plurality of dewatering devices successively arranged in a web travel direction, where adjacently positioned dewatering devices are spaced from each other, and each dewatering device is arranged to direct a gas pressure onto a surface of the web. In this manner, relative to the web, a plurality of pulses are directed onto the surface of the web.
In accordance with the features of the invention, the gas pressure in each dewatering device may be a constant pressure.
The gas pressure in at least one of the dewatering devices can be adjustable independently of the pressures in the other dewatering devices. Further, the gas pressure in the at least one dewatering device can include gas pressure pulses which are adjustable over time. The gas pressure pulses may be adjustable at a certain frequency.
Moreover, the gas pressures in the dewatering devices can be adjustable independently of each other. The gas pressure in each of the plurality of dewatering devices may include gas pressure pulses which are adjustable over time. The gas pressure pulses can be adjustable at a certain frequency.
One of a wire and a felt belt may be arranged on a side of the web opposite the surface onto which the plurality of gas pulses are directed. A membrane may be arranged adjacent the web and opposite the one of the wire and felt belt, such that the plurality of gas pressure pulses are directed through the membrane.
The present invention is directed to a process for dewatering a web in a dewatering zone that includes an apparatus having a plurality of dewatering devices successively arranged in a web travel direction, such that adjacently positioned dewatering devices are spaced from each other. The process includes guiding the web through the dewatering zone, and directing a gas pressure from each of the plurality of dewatering devices onto a surface of the web. In this way, relative to the web, a plurality of pulses are directed onto the surface of the web.
In accordance with the features of the invention, the gas pressure in each dewatering device may be a constant pressure.
The process can include adjusting the gas pressure in at least one of the dewatering devices independently of the pressures in the other dewatering devices. The gas pressure in the at least one dewatering device may include gas pressure pulses which are adjusted over time. The gas pressure pulses can be adjusted at a certain frequency.
Moreover, the process can include adjusting the gas pressures in the dewatering devices independently of each other. Further, the gas pressure in each of the plurality of dewatering devices can include gas pressure pulses which is adjusted over time. The gas pressure pulses may be adjusted at a certain frequency.
The process can also include guiding the web through the dewatering zone with one of a wire and a felt belt arranged on a side of the web opposite the surface onto which the plurality of gas pulses are directed. The process can also include guiding the web through the dewatering zone with a membrane arranged adjacent the web and opposite the one of the wire and felt belt, such that the plurality of gas pressure pulses are directed through the membrane.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.